Systems for applying a viscous foamable mixture, e.g. a mixture for generating polyurethane (PU) foams or polyisocyanurate (PIR) foams, are widely practiced nowadays. Such systems typically have a first (lower) continuously operating belt system, also referred to herein as “laminator”, upon which the viscous foamable mixture is laid down, and a second (upper) continuous belt system for forming so called sandwich panels in between. These panels may e.g. be used for the design of facades on a very wide variety of buildings, alongside sandwich elements for cold-store insulation, etc. The foamable mixture may be a mixture of a polyol and an isocyanate, but it is known in the art that many additives may also be added, such as blowing agents, flame retardants, etc, which are mixed in one or more mixing heads. From the mixing head(s) the viscous fluid mixture is brought to the distributor bar, from which the mixture is distributed over the width of the laminator.
Ideally the viscous fluid mixture is deposited on the laminator in such a way that it creates a uniform mixture layer, but, as is known in the art, designing a distributor bar capable of providing such a uniform mixture layer, is far from trivial. This is especially true for high speed laminators, e.g. having a laminator speed between 20 m/min and 100 m/min, or between 50 m/min and 100 m/min.
WO2009/077490 and US2011/0003082 describe a static distributor bar (see FIG. 1) which allegedly provides a foamed material with less voids and less surface defects as compared to a foamed layer made by using an oscillating rake applicator. Apart from listing very broad parameter ranges, this application gives no guidance about potential problems of laminators, and/or how good laminators are to be designed.
US2010/0080900A1 describes a method for producing composite elements based on foams based on isocyanate. The publication provides some parameters which may be optimized with the intention to keep the velocity of the reaction mixture in the tube or on exiting the holes constant, however, the application does not offer a concrete solution of how exactly that intention can be achieved. Given the large number of variables which need to be defined, the suggested solution is actually a multi-dimensional problem which cannot be easily solved without undue burden.
WO2013/107742 describes another device (replicated herein as FIG. 2) for applying a foaming reaction mixture onto a layer, whereby a central axis of the casting rake (another name for a distributor bar) forms an angle <=80° relative to the axis of movement of the laminator.
US2013/0280538 describes yet another device (replicated herein as FIG. 3) for applying a liquid reaction mixture, whereby the outer openings are directed outwardly under an angle of 1° to 50° with respect to a direction perpendicular to the laminator.
All prior art systems have as a goal to lay down a mixture layer that is as uniform as possible over the entire width of the top layer (e.g. sheet or laminator), but all seem to fail to describe in sufficient detail how this goal is to be achieved. While this goal may be relatively easy to achieve for relatively low laminator speeds (e.g. less than 10 m/min) in combination with a foamable mixture with a relatively low reactivity (e.g. having a cream time higher than 10 s), this goal is not automatically achieved, and actually becomes a real technical challenge at relatively high laminator speeds (e.g. above 20 m/min or above 30 m/min or even higher), or stated differently at a flow rate of the foamable liquid mixture of at least 0.100 L/s per meter length of the distributor bar, especially when viscous foamable mixtures are used with a higher reactivity (which is usually the case for production lines with higher laminator speeds). A distributor bar for such high laminator speeds (or formulated without referring to the line speed: a distributor bar for providing such a high flow rate per unit length) really needs to be specifically designed, or otherwise non-uniformities, e.g. unevenness and/or density gradients and/or knit lines and/or even gaps will occur in the foamed layer.